<!DOCTYPE html>
<html lang="zh">
<head>
	<meta charset="UTF-8" />
	<meta name="viewport" content="width=device-width, initial-scale=1.0" />
	<meta http-equiv="X-UA-Compatible" content="ie=edge" />
	<title>Document</title>
		<style type="text/css">
			*{
				padding: 0px;
				margin: 0px;
			}
			.box{
				display: flex;
				height: 300px;
				border: 1px solid #000000;
			}
			.box div{
				height:200px;
				margin:0 20px;
				background: #00FFFF;
				border: 1px solid #000000;
			}
			.box div:nth-child(1){
				width: 50px;
			}
			.box div:nth-child(2){
				flex: 1;
			}
		</style>
</head>
<body>
	<div class="box">
		<div>1</div>
		<div>2</div>
		<div>3</div>
	</div>
</body>
</html>